1. Field of the Invention
The present invention relates to resin-molded articles excellent in resistance to permeation of gases and/or liquids. Particularly, the invention relates to the resin-molded articles made up of combinations of a polyolefin resin and a polyamide resin and having markedly excellent resistance to permeation and fabrication quality.
2. Description of the Related Art
Polyolefin resins such as polyethylene and polypropylene are widely used as most common plastics for many miscellaneous goods, playthings, mechanical parts, electrical and electronic parts, automobile components, and so forth. In recent years, however, resin products requiring barrier properties to gas (resistance to permeation of gas) are increasing for the purposes of safety, storage stability, and further prevention of contents from leaking to ensure prevention of environmental pollution. Among these, as for automotive fuel tanks the conversion of metallic tanks to plastic tanks has been intensively studied in view of lightness in weight, easy fabrication, freedom of design, and easy handling, etc. Furthermore, it has come to be recognized that prevention of container contents from leaking are of importance to ensure the safety, the storage stability, and the prevention of environmental pollution. As a result, development of materials having resistance to permeation has been demanded. However, polyolefin vessels from polyethylene or polypropylene, which are the most common plastic vessels, fail to have sufficient barrier properties to gasoline and special oils and are frequently limited in applications, and the improvement thereof is expected.
As a method to improve this it is proposed that a thermoplastic resin such as polyamide having high barrier properties is blended with the polyolefin resin to form an alloy. However, simple formation of the alloy fails to improve sufficiently the barrier properties and does not necessarily lead to substantial solution to the problem.
Furthermore, as a special method of alloy formation, a method for dispersing a resin having high barrier properties into the polyolefin resin in a layer state is proposed (e.g., Japanese Patent Publication Nos. 14695/1985 and 296331/1992) and contributes greatly to improvement in the barrier properties. However, the dispersion of the resin having high barrier properties in a layer state as disclosed therein is carried out by extrusion molding (the melt is further stretched after extruding) and has a disadvantage of limiting the shapes of products to sheets or tubes and having insufficient fabrication quality.
The invention, which has been carried out to improve the barrier properties of the polyolefin resins while utilizing the nature of the resins such as toughness and fabrication quality, aims at providing resin-molded articles having excellent barrier properties to liquid chemicals and gases.
The invention provides a resin-molded article comprising a polyolefin resin (a) and a thermoplastic resin other than the polyolefin resin (b), and when depth of the direction vertical to the surface of the molded article is defined as a thickness, as morphology observed under an electron microscope in the resin-molded article, a portion where the polyolefin resin (a) forms a continuous phase (A), a portion where the resin other than polyolefin resin (b) forms a continuous phase and the polyolefin resin (a) forms a discontinuous phase (B), and a portion where the polyolefin resin (a) forms a continuous phase (A) are successively observed in order from the one surface toward the other side in the thickness direction, and also a process for producing the resin-molded article by melt-molding a resin mixture comprising from 20 to 80 weight percent of the polyolefin resin (a) and from 80 to 20 weight percent of the thermoplastic resin other than polyolefin resin (b) wherein a melt viscosity ratio defined by the following formula (1) at a fabricating temperature is 0.5 or less at an arbitrary shear rate of 200 secondxe2x88x921 or less and 0.8 or more at an arbitrary shear rate of 1000 secondxe2x88x921 or more.
Melt Viscosity Ratio=[Melt Viscosity of Thermoplastic Resin Other Than Polyolefin Resin]/[Melt Viscosity of Polyolefin Resin]xe2x80x83xe2x80x83(1)